There are a lot of factors that affect how long milk is good for after the sell-by date. The biggest is whether the milk has been through pasteurization, which John A. Lucey, director of the University of Wisconsin’s Center for Dairy Research in Madison, defines as “the process of heating every particle of milk or milk product in properly designed and operated equipment to any of the specified pasteurization time/temperature combinations designed to destroy all human pathogens” in a 2015 paper published in the journal Nutrition Today.
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